Battery module and battery system having the same

1. A battery system comprising: a plurality of battery modules, each of the battery modules including: an external power supply terminal; a battery cell; a monitoring circuit configured to monitor a residual capacity of the battery cell; a switch circuit configured to supply one of an electric power supplied from the external power supply terminal and an electric power supplied from the battery cell to the monitoring circuit based on a switching signal; and a control terminal; and a controller configured to supply a control signal to the control terminals of the plurality of battery modules, wherein the monitoring circuit is further configured to supply a state signal that is indicative of a residual capacity of the battery cell to the controller through the control terminal, wherein the controller is further configured to select one of the battery modules based on the supplied state signal, wherein the controller is further configured to supply the control signal to the control terminal of the selected one of the battery modules, and wherein the monitoring circuit of the selected one of the battery modules is configured to generate the switching signal in response to the control signal so that the electric power is supplied from the battery cell to the monitoring circuit.

2. The battery system as claimed in claim 1 , wherein the controller is further configured to generate the control signal so as to level the battery residual capacity among the plurality of battery modules.

3. The battery system as claimed in claim 1 , wherein the selected one of the battery modules has a largest residual capacity among the plurality of battery modules.

4. The battery system as claimed in claim 3 , wherein the controller is further configured to select another one of the battery modules based on the state signal, and to supply the control signal to the control terminal of the selected another one of the battery modules, and wherein the monitoring circuit of the selected another one of the battery modules is further configured to generate the switching signal in response to the control signal so that the electric power is supplied from the external power supply terminal to the monitoring circuit.

5. The battery system as claimed in claim 4 , wherein the residual capacity of the selected another one of the battery modules is less than a predetermined residual capacity.

6. The battery system as claimed in claim 5 , wherein the predetermined residual capacity is an average value of the residual capacities of the plurality of battery modules.

7. The battery system as claimed in claim 1 , wherein the controller is further configured to assess variation in the residual capacity among the plurality of battery modules.

8. The battery system as claimed in claim 7 , wherein the controller is further configured to supply the control signal to the control terminal of at least one of the battery modules when the assessed variation exceeds a predetermined value so that the electric power is supplied from the battery cell to the monitoring circuit in the at least one of the battery modules.

9. The battery system as claimed in claim 8 , wherein the at least one of the battery modules includes a battery module having a largest residual capacity among the plurality of battery modules.

10. The battery system as claimed in claim 8 , wherein the at least one of the battery modules have the residual capacity that is larger than the average value.

11. The battery system as claimed in claim 1 , wherein each of the battery modules further includes positive and negative electrode terminals that are each provided separately from the external power supply terminal, and wherein the battery cell is connected between the positive and negative electrode terminals.